A radiotelephone system including a base station for serving remote subscriber stations is described in U.S. Pat. No. 5,119,375. In that system each subscriber station was equipped with a radio that could be instructed by the base station to tune to a particular channel and to employ a particular time slot for the duration of a given conversation. Time division multiplex (TDM) radio channel transmission was employed from the base station to the subscriber stations and time division multiple access (TDMA) transmission from the individual subscriber stations to the base station. The time division of each radio channel into time slots and the compression of speech signals permitted each radio frequency channel to support a number of voice paths equal to the number of time slots. Analog voice signals to and from the public switched telephone network were first converted to 64 kbps μ-law companded pulse coded modulation (PCM) digital samples. Before transmission over the radio channel the digital samples were subjected to voice-compression to reduce the voice information rate from 64 kbps to 14.6 kbps using residual excited linear predictive (RELP) coding. A voice codec and modem were required to be dedicated to a specific frequency and time slot for the duration of a call.
While the foregoing system operated in a highly satisfactory manner in allowing telephone service to be provided especially to areas where wire lines are impractical, the unforeseen growth of such telephone service has given rise to situations in which several subscriber stations are found to lie in close proximity with one another. Initial efforts to lower the per-line cost of serving a group of such closely situated subscriber stations were focused on consolidating the installation and maintenance costs of individual subscriber stations through the sharing of common equipment such as the enclosure, power supply, RF power amplifier and antenna. Thus, in a closely situated group of subscriber stations, each of which could access an RF channel, a single broadband RF power amplifier could be employed to serve the group. However such efforts still required each subscriber line to have its own modem and radio transceiver. The individual transceiver outputs were fed to the common RF power amplifier, which had to be designed to handle a peak power equal to the sum of the power of all of the transceivers in the group of adjacent subscriber stations that could simultaneously be active on the same time slot. It is apparent that further consolidation over that possible in the '375 patent system and a reduction in the peak and average power required would be desirable, especially in remote areas required to be served by solar cell power.